Is this a good blackwater setup?

For the past few months I have been researching a lot what I need to know about keeping aquarium fish and the mistakes commonly seen in beginner aquarists.

For 8 years I had a pet rabbit that died this year and after that I was not sure what to keep but then I found the youtube channel called Foo the flowerhorn which inspired me to want to keep fish.

Because I have aspbergers syndrome this is now one of my many special interests alongside things like computers , nature , and science.


I have decided to keep a 160 liter blackwater biotope tank with lot's of floating amazon frogbit plants , driftwood made out of wild collected oak wood that will be boiled, and most importantly a carpet of dried oak leaves on a bed of sand.

In terms of species I have decided to keep 6 cardinal tetras , 6 xray tetras and one banjo catfish at the bottom to keep it lightly stocked.

All of these species were carefully selected and researched extensively and both live in the amazon river tribunary called Rio negro which is the blackwater biotope I will be recreating.

I live in the swedish countryside where trees and leaves are abundant especially oak tree branches and oak leaves so that is certaintly not an issue in terms of finding aquarium botannicals.

How often would I have to do water changes once the tank is cycled and how many specimens of the above mentioned fish species can I keep at once?

Is this a manageable project or should I consider a different biotype? because of things like ease of cleaning which can be an issue sometimes in a blackwater setup

Sounds interesting. I have a 55 gallon tetra tank with neon, ember and red eyed tetras along with 2 albino catfish. Tetras like to be in shoals of at least 6 so you are doing great so far. I plan on no more than 30 fish in my tank at a time so you will have plenty of room. Once the tank is cyled a water change once a week. If you go on line you will see many opinions on the amount 25%-90% When I had only 1 shoal of fish (red eye) I did around 20-25% in a heavily Planted tank I have increased it as I increased the number of fish but I was also doing a silent cycle, Now I do around 40% a week and of course water testing

Sounds like youve done your research which is awesome.generally one wants to do water changes once a week of around 20% more frequent and higher% depending on bio load. Dark water is also pretty soft water low PH and low GH. Depending on what kind of water you use will depend on how time consuming it will be to achieve " dark water" if your local tap water is hard then it will take more to get the water softer. If local water is soft not as much. If one uses RO water which is basic at 7.0 then getting it low wont require alot either. Ive seen lfs stores carry commercial "dark water" in a bottle and some use peat moss to achieve dark water. Id find out exactly the GH and PH of the water you are using then going from there to determine what you need to get the water below 7.0 PH and low GH

Id also go check out the planted tank forums on this board i think theres a blackwater section.

Welcome to TFF.

A 160 liter (42 gallons) is a good choice, especially if it is 36 inches (90 cm) in length. This makes a big difference. You definitely want to increase the size of the species groups; you have the space, and they will appreciate it and be healthier. Both cardinal and Pristella (X-Ray) tetras cold be in groups of 9-12. And there is space for others too.

First thing you/we need to know is the GH, pH and KH of your source water. Blackwater has basically zero GH and KH with a low (acidic) pH. These values are the critical ones for the fish, regardless of whether you actually aim to tint the water or not. My blackwater tanks have no tinting aside from what naturally will occur with wood and dried leaves. While you certainly do not need to be as accurate in the GH/pH as this, you do need to be very soft and acidic, so knowing the source water parameters will sort out how much work this may or may not need.

Water changes should be more substantial though, 50-60% of the tank volume once each week is minimum. I do more than this, about 60-70% once weekly. I have basically "blackwater" coming out of my tap so this is not a problem, but having to prepare water outside the tank for water changes can be onerous.

On the oak wood, I would not boil it; this can break the fibers apart and rot the wood more quickly. And to be honest, boiling won't really deal with toxins in it anyway. Make sure it is completely dead dry when you collect it, throughout. And collect it from a safe place, away from industry, roads, pesticides, fertilizers, etc.

Substrate hasn't been mentioned, and I would recomend sand, and common play sand is ideal. Safe for all fish, realistic, and very inexpensive. The photo below is my present blackwater, in a 29g tank.

That sounds almost perfect if you have access to soft water. You may want to consider a corydorus species. Corydorus Adolfoi is from the Rio Negro. Another one to consider is nannostomus marginatus (dwarf pencilfish). Malaysian trumpet snails are not biotopic but have a massive biological benefit, especially if you are looking to achieve low maintenance.

I would not boil the wood. This can soften the fibers and cause it to disintegrate faster. The best way to deal with wood you have collected is to leave it in a bucket of water for a few weeks, assuming it was compeletely dry. Once established a blackwater tank is fairly low maintenance. The low light and frogbit should mean that you have very little algae. In my blackwater tank I do a weekly water change (I change 75%) and rinse my filter media weekly. I occasionally wipe the front glass - about once a month. The other walls I leave for the fish.

All of the species I mentioned, plus the tetras, are best in larger groups. 6 is the minimum but their behaviour really is much more natural in larger groups. I would think a good target for this tank would be 15 each of the tetras, corys and pencilfish. But of course it is your choice as to what you keep. Good luck with it if you decide to go ahead.

Byron said:

Welcome to TFF.

A 160 liter (452 gallons) is a good choice, especially if it is 36 inches (90 cm) in length.

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452 gallons??? Wowzers thats big!!!
I think you meant 45 gallons lol.

utahfish said:

452 gallons??? Wowzers thats big!!!
I think you meant 45 gallons lol.

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Yes, thank you, I will correct the typo, it should be 42g for a 160 liter, more or less.

Byron said:

Yes, thank you, I will correct the typo, it should be 42g for a 160 liter, more or less.

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Youre welcome, i was confused for a minute, i was like Byron is smart if he says 160 liters is 425 gallons then im doing my conversions wrong.
Glad to know im not losing my mind lol